The present invention relates generally to vision testing apparatus, as well as a method of testing vision, which makes use of a light-occluding housing having vision testing transparencies movable into a viewing position relative to a viewing area and having a light source to illuminate the transparencies for viewing. In an important aspect of the invention, the illumination source is color-corrected in order to achieve translumination of an especially white character to provide maximum contrast, high resolution and true color rendition for accomplishing visual evaluations that are of enhanced accuracy and reproducibility.
Vision testers that incorporate light-occluding housings and illuminated transparencies have been available for many years and are used for a number of purposes particularly in the area of testing individuals in connection with obtaining driving licenses. Including this extensive use as well as other uses, such apparatus tests far point acuity, depth perception, color perception, lateral-vertical phoria, near point acuity and lateral near point phoria. The relatively simple construction of these testers as well as their versatility establish a substantial demand for them by governmental agencies, schools, opthamologists and optometrists.
The human eye is a living optical system and its characteristics vary widely from individual to individual and, for a given individual, may vary from day to day and even hour to hour. The ability to recognize small, fine details is visual acuity. Normal acuity is defined as 1.0, or more commonly expressed as 20--20 vision. The basic problem is to establish "normal" conditions in the testing of eyesight. The basic standard which has been sought after is commonly referred to as high noon sunlight under ideal conditions, but to test only under such actual sunlight conditions is impractical, if not impossible since artificial illumination must be used. Visual acuity is a function of object brightness. At low illuminations the eye is colorblind. Maximum contrast enhances acuity. Reducing the contrast of the target will also reduce acuity.
As a part of this invention it has been found that the most effective testing of acuity and other properties of the eye is obtained when the light source casts an illumination that synthesizes the noon daylight condition. The governing factor is the amount of energy which reaches and triggers the retina cell into responding. The eye is a poor photometer inasmuch as it is very inaccurate at judging the absolute level of brightness, but it is excellent in comparing brightness or color of two adjacent areas. Thus, variation in brightness contrast is an excellent basis for vision testing but this has not been adequately achieved by equipment now available.
The light sources or bulbs used in current vision testing equipment of the type under consideration have commonly been coated white. It has been found that the illumination provided thereby in this type of equipment, however, is not true white; for example, at approximately 108 volts the light emitted or transluminated has an orange tinge while at 132 volts the light becomes more yellow. Average voltage supplied to homes and commercial establishments is approximately 117 to 120 and the supply will vary, sometimes considerably depending upon demand, and it is not infrequent that surges result. Thus, the quality of the light or illumination used in the type of testing apparatus under consideration can constitute the weakest and most changeable function of such apparatus and, therefore, can create a serious problem as far as effective use of such apparatus is concerned.
In summary, the present invention deals with an improvement in vision testing and apparatus therefor, such apparatus including a light-occluding housing having vision testing transparencies movable into a viewing position relative to a viewing area, and light source means positioned relative to said transparencies to illuminate same for viewing. The improvement involves the provision of colored filtering means interposed between the light source and the viewing area, with the filtering and light source means cooperatively providing illumination that substantially simulates daylight conditions. In an important aspect of the invention, the filtering means is blue colored and the illumination is in the range of approximately 5000 to 5500 degrees K. The subject invention deals with a vision tester having a color-corrected illuminating system which will simulate ideal daylight lighting conditions as accurately as possible and will minimize detectable variations therein over the range of voltage variations that are typically encountered by this type of apparatus and method.
It is accordingly a general object of the present invention to provide an improved vision testing device and method.
Another object of this invention is to provide an improved eye testing device and method with color-correcting characteristics.
Another object of the present invention is to provide an improved eye testing device and method that provide translumination which achieves maximum contrast, high resolution and true color rendition without increasing heat generation.
Another object of the present invention is an improved eye testing device and method that is capable of providing a reproducible illumination standard which is substantially consistently maintained in the face of variations in input line voltage.
Another object of this invention is to provide an improved eye testing device and method that achieves translumination in the range of daylight conditions of between about 5000 and about 5500 degrees K.
Another object of the present invention is to provide an improved method and apparatus for accurately testing night vision, contrast sensitivity, and color perception, and the onset of cataracts.